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Re: [PATCH] virtio-blk: add missing AioContext lock
From: |
Lukáš Doktor |
Subject: |
Re: [PATCH] virtio-blk: add missing AioContext lock |
Date: |
Wed, 8 Feb 2023 13:33:54 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 |
Dne 08. 02. 23 v 12:11 Emanuele Giuseppe Esposito napsal(a):
> virtio_blk_update_config() calls blk_get_geometry and blk_getlength,
> and both functions eventually end up calling bdrv_poll_co when not
> running in a coroutine:
> - blk_getlength is a co_wrapper_mixed function
> - blk_get_geometry calls bdrv_get_geometry -> bdrv_nb_sectors, a
> co_wrapper_mixed function too
>
> Since we are not running in a coroutine, we need to take s->blk
> AioContext lock, otherwise bdrv_poll_co will inevitably call
> AIO_WAIT_WHILE and therefore try to un unlock() an AioContext lock
> that was never acquired.
>
> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2167838
>
> Steps to reproduce the issue: simply boot a VM with
> -object '{"qom-type":"iothread","id":"iothread1"}' \
> -blockdev
> '{"driver":"file","filename":"$QCOW2","aio":"native","node-name":"libvirt-1-storage","cache":{"direct":true,"no-flush":false},"auto-read-only":true,"discard":"unmap"}'
> \
> -blockdev
> '{"node-name":"libvirt-1-format","read-only":false,"cache":{"direct":true,"no-flush":false},"driver":"qcow2","file":"libvirt-1-storage"}'
> \
> -device
> virtio-blk-pci,iothread=iothread1,drive=libvirt-1-format,id=virtio-disk0,bootindex=1,write-cache=on
>
> and observe that it will fail not manage to boot with
> "qemu_mutex_unlock_impl: Operation not permitted"
>
> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
> ---
> hw/block/virtio-blk.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 1762517878..cefca93b31 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -894,6 +894,10 @@ static void virtio_blk_update_config(VirtIODevice *vdev,
> uint8_t *config)
> uint64_t capacity;
> int64_t length;
> int blk_size = conf->logical_block_size;
> + AioContext *ctx;
> +
> + ctx = blk_get_aio_context(s->blk);
> + aio_context_acquire(ctx);
>
> blk_get_geometry(s->blk, &capacity);
> memset(&blkcfg, 0, sizeof(blkcfg));
> @@ -917,6 +921,7 @@ static void virtio_blk_update_config(VirtIODevice *vdev,
> uint8_t *config)
> * per track (cylinder).
> */
> length = blk_getlength(s->blk);
> + aio_context_release(ctx);
> if (length > 0 && length / conf->heads / conf->secs % blk_size) {
> blkcfg.geometry.sectors = conf->secs & ~s->sector_mask;
> } else {
Thanks, I can't talk about the correctness of the code but function-wise it
addresses the issue.
Tested-by: Lukáš Doktor <ldoktor@redhat.com>
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